This is a competing continuation proposal, based on recent findings by the PIs that most of boys' aggression occurs within a small number of dyadic relationships. The major aims of this project are: 1) to develop a reliable and valid method of identifying, aggressive dyadic relationships in boys' peer groups in the school setting; 2) to the relation between social information processing patterns (specifically, hostile attributional biases and motivational withdrawal) and dyadic aggressive behavioral exchanges; and 3) to examine the cognition-behavior relation temporally as boys come to be acquainted with each other. Three studies will be conducted. The first study is directed toward the reliable and valid identification of several types of dyadic relationships in boys' classroom peer groups. Peer, teacher, self-report, teacher diary, and direct observation methods will be employed to identify and validate different kinds of dyadic relationships, including mutually aggressive, asymmetrically aggressive, low-conflict, and unstable dyads. In the second study, boys in these dyadic relationships will interact with each other in experimental play groups conducted on five consecutive days. Boys' hostile attributional biases and motivational withdrawal toward dyadic partners will be related to their socially interactive behaviors with these partners in the free play setting of these groups. It is hypothesized that boys who display hostile attributional biases and motivational withdrawal toward a dyadic partner will aggress frequently and angrily toward that partner. In the third study, the temporal relation between social information processing patterns and aggressive behavior in dyads will be assessed by asking previously unacquainted boys to interact for five play sessions in consecutive days. Daily interviews will assess attributions and motivation toward dyadic partners. It is hypothesized that hostile attributional biases and motivational withdrawal will increase later aggressive conflicts. These studies will lead to a greater understanding of aggressive behavior in dyadic relationships and the role of social cognition in the development of aggressive conflicts. This work will also lead to preventive interventions aimed at reducing aggressive conflicts.